1. Field of the Invention
This invention relates to an apparatus for vacuum deposition which arbitrarily controls the components of a film to be formed by deposition and having component elements of different vapor pressures and which produces the deposited film having a component ratio or a gradient thereof as desired.
2. Description of the Prior Art
Heretofore, in fabricating a vacuum deposited layer of a compound consisting of two or more kinds of elements, the expedient of flashing evaporation or coevaporation employing a plurality of boats has been adopted in order to prevent the deviation of the composition ascribable to the fact that the vapor pressures of the component elements are different. The flashing evaporation is a method wherein a raw material is dropped bit by bit into a boat heated to a high temperature and the dropped bits are vaporized in a short time. With this method, the deviation of the quantities of the component elements from predetermined values is comparatively small. The method, however, is disadvantageous in that defects are prone to occur in the deposited film because the raw material is fused and vaporized abruptly. Besides, it is difficult to satisfy the requirement that the component ratio of the deposited film be changed continuously in the direction of the film thickness.
The coevaporation from the plurality of boats enables to arbitrarily select the components of the deposited film. Since, however, the distances from the respective boats to various points on a substrate for deposition are not equal, the composition ratio becomes non-uniform at various parts of the surface of the deposited film.
In U.S. Pat. No. 3,800,194 is proposed a method which resembles the cyclically accumulating a large number of thin layers of respective components. According to this method, vapor flows from a plurality of vaporization sources are measured and controlled by using an ionization type gauge or a film-thickness monitor, and a film having a desired composition ratio is obtained by the rotary deposition method. The method, however, is disadvantageous in that since a probe for measuring the deposition rate or the deposited film thickness is not situated at a position identical to that of a substrate for deposition, the quantity of the substance actually deposited onto the substrate for deposition and the quantity of vaporization detected by the probe do not always correspond precisely.